President Xi Jinping (習近平) and Japanese Prime Minister Shinzo Abe are several times a year at important international gatherings, as at the nuclear summit in Washington last week. They barely acknowledge each other, though, if at all. Meanwhile, their militaries are expanding and strategic ambitions rising, some would say dangerously so. The lack of communication, even at the most fundamental level between navy captains, increases the risk of an incident spinning out of control.

Disputed islands in the East China Sea and Japanese support for countries involved in separate territorial rows with China in the South China Sea are at the crux of recent tensions. Japan perceives the modernisation of the Chinese military as a threat and Abe uses it to justify increases in defence spending and a reinterpretation of pacifist sections of the constitution. His most controversial move, new national security legislation increasing the scope of Japan’s military operations, took effect last week. Self-defence forces can now join the US and other allies in fighting overseas conflicts.

Which circumstances would justify such deployment have never been made clear. Abe has promised to explain, but has yet to do so. His government exacerbated tensions this week by stating that there was nothing in the constitution that forbids Japan from possessing or using nuclear weapons.

Japan’s defence budget has risen each year since Abe took power in 2012, the latest increase being 1.5 per cent. That appears paltry compared to China’s latest increase of 7.6 per cent, but the Japanese security alliance with the US means its forces have long had more advanced equipment. The opening last week of a radar base 150km from the contested Diaoyu Islands, known in Japan as the Senkakus, further raises tensions.

An arms race is economically counter-productive. Abe’s economic reforms have sputtered and the country is again facing with deflation. China’s slower growth also requires effective use of resources. The region needs stability, not uncertainty. China and Japan, as Asia’s biggest economies with extensive trade ties, need to closely interact and communicate at all levels. Foreign Minister Wang Yi (王毅) and his Japanese counterpart, Fumio Kishida, met in Washington, but it is talks between Xi and Abe that will have the greatest impact on fraught relations. There are opportunities later this year when China hosts the G20 summit in Hangzhou in September, or at the China-Japan-South Korea trilateral leaders’ meeting, to be held in Japan.